Primary debug scenario

Symptom: USB device not enumerated. PHY shows device attach detect. No USB traffic.

Triage steps

1. Check device controller clock and reset.

2. Verify PHY reference clock and power.

3. Scope D+/D- for chirp sequence (HS negotiation).

4. Check if device firmware is running and responding to setup packets.

5. USB analyzer: any activity on the bus at all?

Common pitfalls

• Descriptor mismatch: firmware reports capabilities silicon doesn't have.

• Missing pull-up on D+ (FS) or D- (LS) for device detect.

• Rewriting driver before checking PHY and device firmware.